HP StorageWorks XP Remote Web Console Software - Manual (Page 23)

Continuous Access XP Journal user guide 23
Remote copy operations
Figure 5 illustrates the types of Continuous Access XP Journal remote copy operations: initial copy and
update copy.
Figure 5 Remote copy operations
Initial copy operations
Initial copy operations synchronize data in the primary data volume and data in the secondary data
volume. Initial copy operations are performed independently from host I/Os when you create a data
volume pair or resynchronize a suspended pair. The initial copy operation copies base-journal data
obtained from the primary data volume at the primary disk array to the secondary disk array, and then
restores the base-journal to the secondary data volume.
If the journal-obtain operation starts at the primary data volume, the primary disk array obtains all data of
the primary data volume as the base-journal data, in sequence. The base-journal contains a replica of the
entire data volume or a replica of data volume updates. The base-journal is copied from the primary disk
array to the secondary disk array after the secondary disk array issues a read-journal command. After a
base-journal is copied to the secondary disk array, the base-journal is stored in a restore journal volume in
a restore journal group to which the secondary data volume belongs. After that, data in the restore journal
volume is restored to the secondary data volume, so data in the secondary data volume is synchronized
with data in the primary data volume.
The base-journal data is stored in the entire data volume or the area for the difference. The area for the
difference is used during differential resynchronization operation. The journal data for the entire data
volume is created when the data volume pair is created. The difference journal data is obtained when the
pair status of the data volume changes from Suspending to Pairresync. Merging the difference bitmaps
recorded on the primary and secondary data volumes allows you to obtain differential journal data for
only. When a data volume pair is suspended, the status of data that is updated from the host to the
primary and secondary data volumes is recorded to the difference bitmap.
The base-journal data of the primary disk array is sent to the secondary disk array journal volume after a
read command has been issued from the secondary disk array. After that, the base-journal data is restored
from the journal volume to the secondary data volume. The initial copy operation finishes when all
base-journals are restored.